Wind tunnel balance



H. M. Hx-:UVER

WIND TUNNEL BALANCE Sept. 7, 1948.

6 Sheets-Sheet l Filed May 2, 1944 NIIILII IN VEN TOR W Mm @m E A n www w. w vw, f w

Sept. 7, 1948.

Filed May 2, 1944 FIG.2

H. M. HEuvER 2,448,528

WIND TUNNEL BALANCE 6 Sheets-.Sheet 2 Sept 7, 1948 H. M. HEUVER 2,448,528

WIND TUNNEL BALANCE A INVENTOR Hf M. HEUVER WIND TUNNEL BALANCE Sept. 7, 194.8.

Filed May 2, 1944 6 Sheets-Sheet 4 FIG. 5

, INVENTOR HEPBEET/V. #ful/@ BY A k ATTORNEYS Sept. 7,- l94& H. M. HEUvl-:R 2,448,528

WIND TUNNEL BALANCE Filed May 2, 1944 6 Sheets-Sheet 5 FIG. 7

FIG.8

#ERBE/effi Heal/ER Sept. 7, 194& H. M.' Hx-:uvl-:R

WIND TUNNEL BALANCE 6 Sheets-Sheet 6 Filed May 2; 1944 IN VE N TOR H5255@ 7- M H5 U//f A TTRNE YS Patented Sept. 7, 1.948

U NI TED! STATES? F FICE ariane wmp TUNNEL .BALANCE HerbertMa Heuvel', Dayton, Ohio', Applica-.imma 2; 19m/senatore.; 533,186'.

(o1. vs -447)y (Granted under the vact oiiV March 3,2 1883, asl

amended April. 30, 1928;; 370.- 0.- Gr.. 757.)

The invention' described:l hereinmay be1 manu-- factured Iandz used by or for the'Grovernmenl-iv for governmental purposes, Withoutthe payment-to me of any royalty thereon..

This invention refers tov balances-.for Wind tunnels and especially to balancesV adapted to: multiple component` measurement.

Various wind' .tunnel balances have been propiosed: in the past for*v measuring the forces and moments exerted on a model: exposed tothe moving air stream in the tunnel and: in certainrA of those balances-'such asthe six-component balance andV in the various Wire suspension methods, it Was possiblefto;v directlyv read the. actual forces and moments exerted on-. the model; but such balances arefnot as:` adaptable'. for properly supporting the vmodel in ther air stream ofia`- wind tunnel. In testing modelsf and-full sizev aircraft in Wind tunnels it is necessary to provide a very substantial supporting structure for the model or airplane under test,.,andv thearequirementsfare generally such that the modeLor aircraft. being. tested must be supported at a considerable elevationabove the Weighing mechanism-r Irrsuch balances, as I am at presentaware, it.' hasvnotcl been possible to directly read. all'A ot theA forces. and. moments exerted on thev4 model or aircraft under. test and it has been necessary-to. correct thefbalance readings for Amoments introduced-:dueto the elevation of the model-above the weighingmecha- CTI nism which requires considerable.additionallcomputation upon the completion-off a .test to detenmine the actual forces and: momentsexerted on the model or full size aircraft.

I-t is therefore an objectof: theinventinlto provide a Wind tunnel balance suitable fon testing models or full size aircrafttinqwhich all-of the forces and moments.actingonthemodelcan be read directly onthebalance scales .without-requring the application-otcorrection factorstofthe readings to allowfor theeffects of-momentseintroduced by the model-suspension system.

A further disadvantage off balancestructures at present in use for testing modelsfor full -size aircraft lies in thefactfthatf allfmoments..occur-y ring on the model or aircraft -being tested-aragonerally taken about azpoint :other than" th'es center of gravity location on the modelfrepresentingxthe center of gravity; locattonbot4 the: fullsize aircraft; and accordingly, it isf-necessary.u to-recomputefall moments. in order .tovtransferthefsame tofgive the moments about the centerofv gravit-yi of',` the full size air-plane,` which involvesaa-'tgreat deals-of numerical computation; Inzaccoi'dance=with'zthe present. in-vention,1means.; are providedli whereby axis-off the airplane or.-4 model being' testedmay be" positioned at any desired point with respect to themoment: center ofi the balance system,. that isg. the moment` may. be' taken either aloiouti` the quarten'chord point of: theiwing or aboutl the cen'-I terofi gravity location, or about any other axes desiredgso thattheread'ings of thebalancesrneed' not be corrected inl. rorderto: determine the mo'- mentsabolut somedesired point or axis upon the model being tested. This feature resultsy inthe saving1ofl a. large amount of tedious computation Work and facilitates` the interpretation of the test results in a minimum of time. l

It. is. therefore [another object o=` the' invention toyprovidein combination, a balance'giving direct indications of allv of theforcesand momentsexexited-.upon amodel and means for adjustingthe position ofv aselected axis on' the model With= re.- spectv to al fixed moment center of the balance system, Whereby'themoments exerted about any desired: axis'of` the aircraft may be directly.` determinedr from thereadings on the'balanc'esystem:

Other objects and details of the invention Will becomefapparent tot-hose skilled in the art by reference to the Vdetailed o description hereinafter given and to the appended drawings in which:

Fig. 1" illustrates schematically a top-plan of a wind tunnel` balance constructed in accordance with the inventiom'with the floating frame indicated in dotted lines for clarity of illustration;

Fig. 2fillustrates avieW partly in sectiontaken on line-.x-- of Fig. 1;`

Fig. 3 is anV end View partly in section taken Online y-yof'Fig. 1;

Fig; 4 is afnagfment'ary view illustratingrthei details/of aw semi-universal rod terminal employed in` the invention;

Fig- 5i is an isometric view illustrating those elements o1v the balance of' Fig. 1 employedV in measuring-the drag force,` and the'pitch moment exerted on'` a* model supportedA from the balance systema Fig. 6 is ai diagrammatic View illustrating the principlefoff compensation of' the 'balance ofV Fig; 1r for' eliminating pitching moments caused by drag forcesv exerted'through' the model' suspension. system Fig; 7i is aview'similar toli'g.. 5 illustrating the side" force.. rollingl moment and' yawing moment measuring system of the'balance of Fig. 1;

Fig. 8 isra view similarto Fig. 6 which illustrates the application offthe'means for compensating. for` the effect lofi moments' introducedl in the balance due to the side force acting through the model suspension system; and

Fig. 9 is an isometric view illustrating a means for adjusting the position of a selected moment axis on the model with respect to the moment center of the balance illustrated in Fig. 1.

Referring now to Figs. 1 to 3, the reference numeral I illustrates a concrete or other enclosure positioned beneath the throat of a wind tunnel (not shown). This enclosure is adapted to enclose the balance mechanism and means for transmitting forces and moments thereto, and also serves to support the fixed parts of the balance mechanism. The reference numeral 2 indicates -a base structure on which is mounted a suitable model support generally indicated by the ref erence numeral 3. The base structure and model support (see Fig. 2) are herein merely conventionally illustrated, but actually include mechanism for moving the model support to shift the model with respect to a fixed moment center which forms an axis or point in space, as Will be hereinafter more fully described with respect to Fig. 9. In discussing the balance mechanism, it Will be, for the present, considered that all forces and moments to be measured by the balance system will be transmitted from the model to the vertical support 3 for further transmission to the balance mechanism through the base 2.

The base 2 is adapted to be secured to a rectangular open frame 4, hereinafter referred to as a floating frame', since the same is adapted to move upward, rearward or sideways, due to the exertion of lift, drag or side force, respectively, or is adapted to rotate about either axis rmx or y-y of Fig. 1, or to rotate about the vertical axis 2 2, Fig. 2. In other words, the three possible forces and the three possible moments which can be exerted on a model tend to produce a similar linear or rotary movement of the floating frame 4. ,A

Floating frame 4 is supported by means of -four vertical rods 5, 6, 1, and 8 respectively, each positioned at one of the corners of the frame. Y The rods to 8, inclusive, are adapted to transmit only axial for-ces, this being insured by employment of a semi-universal rod joint or terminal such as illustrated in Fig. 4, in which ats such as I2 and I4, spaced apart by an intermediate section such as I3, allow free movement of the rod in planes at right angles to each other but permit the transmission of axial forces along the axis of the rod. Throughout the discussion of the structure hereinafter given, it will be assumed that rod joints of this type are employed on all members designed to transmit only axial loads. It will be seen that all vertical forces acting on the model will be transmitted through base 2 and floating frame 4 to the rods 5 to 8, inclusive, so that the sum of the for-ces in the rods is a measure of the liftacting in the direction of the Z axis (Fig. 2) exerted by the model. Although the forces in the respective rods may differ, due to the application of moments or couples transmitted from the model, the sum of the vertical loads in the rods will always equal the lift. The rods at their lower ends are connected to bell cranks I5 to I8, inclusive, each of which is supported by means of a knife edge 26, preferably of the flexible type, mounted on a rigid support 2i, in turn supported by the foundation of the balance. It will be seen that while the rods 5 to 8, inclusive, are capable of transmitting lift forces, due to the fact that the rods are provided with semi-universal terminals such as illustrated in Fig. 4, they will be unable to resist any horizontal motion of the iloating frame 4. `The s and connected at its outer end to a conventional lift balance 34 of the well-known automatic bal- .ancing recording type; that is, upon any change in load on the balance, an electric motor is auto- 'matically set-into the action to bring the balance rapidly into equilibrium with the existing external loads, the balance being adapted to print V the totalforce measured thereby on a tape at any time at the will of the operator, such automatic balances being well-known in the art and per se forming no part of the present invention. It will thus be seen that all lift forces will be transmitted from the floating frame 4 through the rods 5 to 8, inclusive, which in turn will be transmitted through the bell cranks I5 to I8, inclusive, respectively, with a change in direction and magnitude depending `upon the mechanical advantage of the respective bell cranks and converted into axial forces in the respective rods 23 to 26, inclusive, so that the vertical component of the loads in each of these rods will be applied as a down force on the floating lever 3E and transmitted from said column to the rod 32, from whence the same will be transmitted by balance arm 33 to the lift balance 34 which Will record the total lift force acting on a model supported on the vertical support 3. The geometry of the balance is so determined that the balance will measure all forces and moments about the axis or point of space 6, Figs. 2 and 3, which for any balance will -be -determined by its respective design and maybe made as desired to suit testing conditions.l

In addition to transmission of lift forces which are the vertical components of the axial forces appearing in rods 23 to 26, inclusive, it will be noted that the rods 23 to 26 are each capable of exerting horizontal forces in two planes onA the floating lever so that, in addition to the effects of lift, for-ces maybe exerted on the floating column du'e to the difference in the horizontal components of the force existing in the respective rods 23 to 26, inclusive. I'This difference results from the application of external moments to the model support 3 from air stream forces acting on the model.

The floating frame 4 is provided with two lugs or ears spaced on opposite sides thereof (note Fig. 1) suchl that any forces'acting along the plane of XX, Fig. 1, will be transmitted by rods 3'I and 38 universally connected to the respective lugs and 36 and will be transmitted through respective bell cranks 39 and 40 which are pivotally supported on knife edges or the like 4I or 42 respectively secured to suitable supports anchored on the enclosure I. The bell cranks 3S and 40 transmit loads from rods 31 and 38 to vertical rods 43 and 44, respectively, which are providedat each end with semi-universal joints of the type of Fig. 4 and are connected at their lower ends to bell cranks and 46, respectively, each of which are suitably pivotallyv mountedlon knife edges supported from the floor of the enclosure. The bell cranks 45 and 46 transmit their force by means of rods..41 and 48, respectively, to a horizontally extending link 481-` (see- Figs. 1; 2*; andi 55@` W'hiclnis4 secured atiits-inner-end tothe-.iloating-lever.- 31E by.- means:off-asemieuniversala jointA of.i the type-off Eig. 4 so that .the rod 494s;capableiofftransrnitting only axial forcetothe floating lever 30 butisnot capable ofv transmitting; turningy or othermoments` thereto. Axial--forcesr-in. t'he-v plane of Fig. l, will be transmitted through rodsJ 311-" andi- 381, bell cranks- 39 and 4 0, verticali rods-431 andi 44a andi belli cranks 45# and 4- to the rodsl 4111? and: 4ll=` fromwhence the same willlbe appliedby means ofrod's 49.y to the floating lever 30. A= rod in the planeioff XX; Fig. 1-, andE positioned'verticallyv above the lingy 41h transmits drag-forcesf-rom theA` lever' 310i to a conventionali automatic balancingY dragI balance 5 |-V of-` conventionalconstruction, theL rod1 501beingsemi-universally connectedv .byy means: of" a joint or the type of' Fig; Q to.- the oating lever 30"" so that no moments may be transmitted either to-orthrough the rod 50. @nthe opposite side of rod 50 and in the `pla-neef XliisrA positioned@ ay rod? .S2-f whichisvuniversally` connected at one end-to lever 30" and serves to transmit` forces asfameasurel oivv moments intheplane of XX froml thefloating lever- 3UI toaconventional automatic balancing and Arecord-ing balance -54`which recordsthe pitching moment, the rod 52- being connectedv to the lever' 303 at the point off intersection ofI rods 23- to- 26, inclusive;`

The float-ing frame 42 is-stab-l'izedagainst anyv movement in the-plane -oifaz-rc, Fig. 1', caused by dragforce, such asX',l Fig. 21, since the drag bal"- ance- 51 Will:4 supply a reactionr force opposing-- the forces transmitted' theretoV from the linkage system above described'.v It vvilllv benoted; however, byreference'toFigs; 2 andig that the dragy force-Xexerts a moment of (X) (H) on the oating framev 4-, andiL causes an unequall dis--y tribution of loads i-n-the lift rods 5to-lit; inclusive,I Whi-ch-in-turn produces-an inequality of-the horizontal components ofr the forcel in' the lift trans-y mission rods 23' to=2`6g inclusive, which tends-'toproduce a horizontal force"l at the pointof intersection with lever 3'0, which is a1 measure of" the'- moment (2i)` :r (HZ) in the plane MVX-X, Fig. 1, acting on the model-support 3 (note- Fig. 2). It will be also evident that anyf lateral-'r orrolling moments exerted bythe model on the model support 3'; Fig. 2, will in asimilarmanner produce horizontal:forces-.acting on the floating lever 301 By means of the particular arrangement' oi*- the-linkage, the effect-fof the drag force in producing a pitching moment on the floatingv frame 4' islneut-ralized* in the pitch-andi draglink'- age, so that any horizontalforces produced'- by the-moment X'H on the iloatinglever-iU-will be` compensated for by the-horizontal force-transmitted to the floating columnl by the drag linkage, making-the force producedin' rod 52i a measurev of the` pitching momentabout' the moment center-'.

The floating frame 4 is provided with opposit'ely.- positioned lugs 5.5' and- 56' spaced 90 fromV the axis of lugs 35 and';` which have connected thereto by-semifun-iversalzjoints off` the'y type of Eig. 4f the; rods. 51% and4 58;. respectively,` which. rods( are connectedto belll cranks: 59: and; 80, re-I spectively, pivotally supported' by.` knife edges 611v and;v 6,25, respectively,.- (note- Fig: 157)-` which` are anchored-to the walls or; other suitablestation-` ary, structureof.` the-enclosure I-andsallsidefforccl that, is., forces actingin-j the plane( of: axis-.1: 1re-ul, Fig. 1 vvill-` bef transnfiittecr` throughL such rods.- to;

the:` bell.- cranks.. and-y similarly. allturning.- or, yaiv.-

moments. exerteds uponV the heating; frame.- 4t

supportedmeans` of flexible knife edgeslsuchv as. illustrated. at. 671-63, Fig. 3. The bellcranks @5i-$6', Fig. 1, transmit forcesI to horizontally extending rods 619- and'l, respectively, whicharesomt-universally connected at their inner ends .a in aA common pivoted juncture to an arm 'Il' se cured'l tothe oating lever- 304 (note Fig. l.) in a. manner to transmit only axial force thereto. Thek pivoted juncture of,` rods 69- and 'I0 with the-rod Tl is--connected` by means of a link 12 to a yavringr moment balance 15 also of the automatic selfbalancing and recording type, the rod- 12` being providedlv at its ends: withV semi-universal jointsy of? the type of Fig. 4- and therefore can transmit only axial forces tothe yawing` momen-t balance. Immediately 'above they rod 'H1 is positioned a rod 1,6-, which is semi-universally connected at its-- outer endv to the floating lever 3i) and at its innerend is connected to an4 automatic self-balancing andi recording side force-balance 11. On-the opposite side of the side for-ce transmittingrod 16 and in` the plane thereof a.- horizontal universally connected rod 18 is securedto the iioating` l'ever30'l (at they point ofintersection ofrods 231 to.26) such that it may transmit cer-tain forcesactingl onsaidcolumnin the plane ofy-y Fig- 1i, to a rolling moment balance 8D also of theautomatic balancing and recording type.

Since therod- 59, associated with the drag measuring means (previously described) is in- 'fca-pable of transmitting any turning or yawing moment exertedv on the frame 4 to the floating lever '1 and hence iS-incapable of transmittingv counter-reacting forces to the frame 4 from the bal-'ance system; all' turning or'yawing moments exerted on--the-frame 4'. aboutv the axis ZZ, Fig. 2, must lloe-transmitted from lugs and 56, links,- 5f1land` 581andbell cranks 59 and 60 to the vertical rods-Gland- 641' from whence same will appear as components of the respective tension and compressionn forces in the rods 69 and 1D, and'since anyu torque or couple producing turning of the floating frame 4 about the axis Z-Z, Fig. 2, will produce horizontal components of the forces inrods G9* and 10, Fig. 1, which are additive and f their: sum will be a measure of the yawingv moment .exerted on-the frame 4` by the model and it Willms-transmitted through the yawing moment rod 12@ directly toV yawing moment balance 15 which inturn will produce reacting forces counteract'ingany tendency of the frame 4- to rotate ini yaw about axis Z--Z, Fig. 2. In a similar Inanneranyslide'for-ce transmitted to the frame 4'- in` theplane ofv Y-Y, Fig. 1 will also be transmitted-*to rods GSF and-10 such that" the algebraic sum of: .the components of the forces in these rods? in the Y`Y plane will app-ear in rod 1,6

. as afmeasureof the side force which is indicated onbalance 11, however, the arrangement is such that any: rolling momentsproducedby side force acting on4 the modelsupport 3, Fig. 2, andtending; tov cause rotation of the frame 41 about axis XX,Fig. 1willr be compensated in a manner similar tor` that employed in! compensation for pitching moment` dueto drag, and-hence the rolling? momenti balance:- dl will read only actual,

rolling moments exerted on Athemodel andv not those due to side force acting through the distance H, Fig. 2. The means for -compensating for the pitching moment-s due to drag and the rolling moments due to side force will now be more fully described with reference to Figs. and 8, in-

clusive.

The means for compensating for the pitchin moment introduced by the drag force will now be considered in more detail with reference to Fig. 5 in which the elements taking part in the measurement of drag and pitch are illustrated with the remaining structure removed. As seen in Fig. 5 and as previously described, the lugs 35 and 36 secured to the iloating frame 4 are adapted to transmit any forces acting in the plane X-X,`

such as the drag force X through rods 3l and 3B to bell cranks 45 and 46 which then transmit the respective forces through rods 4l and 48 to a single rod r49 provided at its inner end with a semi-universal joint of the type of Fig. 4, at which point it is secured to the floating lever 30. Since the member 49, by virtue of its universal connection to floating lever 3H, is incapable of transmitting a torsional moment thereto even though yawing moments tending to rotate the frame 4 exists, the forces in rods 31 and 353 will be equal since all yawing moments will be reached by rods 51 and 58 and such rotational moments can not be imparted to the lever 3l) my means of rod 49 which is capable only of transmitting axial forces. It is, therefore, seen that while forces may be set up between rods 31 and 38,*due, for example, to the existence of a yawing moment such as indicated by N, the rod 4Q is incapable of transmitting any horizontal components of such forces to the oating lever 30, and since there must be equilibrium in the horizontal plane, the

sum of the forces on rods 31 and 38 must be equal to the actual drag -iol-ce X, which is therefore transmitted except as modified bythe mechanical advantages of the various transmitting bell cranks to the rod 49, and accordingly floating lever 3!! is subjected to the force tending to displace the same in the X plane and suchforce is proportional to the drag force X transmitted tothe frame 4 from the point Il through the model.

suspension system indicated by support 3..' Itis also apparent, as previously described, that the drag force X acts through a distance -H above the frame 4 and accordingly tends. to tilt the framer about the axis Y-Y of Fig. 1 and produce a pitch-` ing moment on the frame. The pitching moment introduced by drag force X on the frame 4 tends to increase the lift forces in rods 5 and l and to decrease the lift forces in-rods S and 8, and accordingly produces similar variation in the forces transmitted through rods 23 and 25, and

24 and 26, respectively. The'horizontal comfponents in the X--X plane of the forces in ren spective rods 23 to 25, inclusive, will so combine additively as to produce a force in the floating lever 3i), due to the pitching effect exerted by the drag force on the iioating frame 4, and it will be noted that this force is applied at the point of intersection of rods 23 to 26, inclusive, and to the iioating lever 30 below the anis of the dragv force transmitting rod 49, and the arrangement is such that compensation is effected so that the This compensation willbe more 81 apparent by reference to Fig. 6 in which it is seen that the horizontal component of the forces transmitted through the lift linkage, due to the pitching moment due to drag in the X plane, is transmitted to the lever 3D at a distance a below the axis of rod 49, and such horizontal. component acts in the opposite direction from vthe force transmitted to rod y49 from the drag linkage. A net force proportional to the drag force is transmitted by link 5U directly to the drag balance 5|, and such link is positioned at a distance b above the point of attachment of the lift linksl design of the structure, distances a and b can be so made in conjunction with the mechanical advantages of the various bell cranks transmitting forces to the floating lever that the force transmitted through rod 49vproduces an equivalent force at the point of intersection of the rods 23 to 2%, inclusive, and opposes the sum. of the horizontal components in the X-X plane of the force transmitted to the lever by llift links 23 to 26, inclusive, due to the pitching moment introduced by the drag force, and accordingly there will be no tendency for the lever 30 to rotate in the plane of X, and the force transmitted through rod 50 to Adrag balance 5I will be a true numerical measure of the actual dragorce X; that is, all values of the force transmitted through rod 50 will be proportional to X. Referring again to Fig. 6, itis, however, apparent that the drag force transmitted to floating lever 30 through rod 49 is capable of producing a force at the point of connection of rod 52 to said floating lever which is equal and opposite to the pitching moment due to the drag force, and if there is any excess pitching moment transmitted to the oating frame 4 from the model suppo'rt 3 in addition to the pitching moment ldue to the drag force, the horizontal components. in the X-X plane of the forces transmitted through rods 23 to 26, inclusive, will be in excess of the forces arising frompitching moment due solely to drag, and consequently such additional force will be exterted upon the lever 30 for transmission by means of rod 52 directly to the pitch balance 54, which will thus measure only the pitching moment on the frame 4 due to forces about the point 0 on the model. By means of the compensating mechanism above described, the drag balance 5l will at all times give a reading directly proportional to the drag, and pitching moment balance 54 will indicate the true pitching moment acting about the moment center 0 due to the aerodynamic forces acting on the model, and if no pitching moment is exerted on the model support about the point 0, the pitch balance 54 will read zero. rlhe same method of compensating for the effect of forces acting on the modelsupport dueto elevation of the model above the floating frame 4 as employed in compensating for the pitching moment due to drag is also employed in compensating for rolling moment introduced by any side force acting on the model, as best illustrated in Fig. 7.

' Referring to Fig. '7 and as previously described above with respect to Figs. 1 to 3, it is apparent that any yawing moment, such as indicated by N, will produce rotation of the floating frame, and this frame will be angularly displaced unless la contrary reaction force is transmitted thereto from the balance mechanism, and similarly any transverse force, such as the side force Y acting in the plane Y-Y, will'produce a transverse displacement of floatingv frame 4, and the forces due either to yawing momentN or side force Y will :be transmitted vfrom the frame4 by means of llugs 55 and 55 through rods 5'!l and 58, bell cranks 59 and 6"!) to vertical rods. 63 and 54 and then by means of bell cranks '65 and S6 to rods 69 yand -10 as previously noted. The rods E9 and 10, as previously noted, are pivotally ccn-n Vnected to the outer end of a rod or larm 'H which is rigidly secured'as by welding to the oating lever 3D, the rigid connection being. employed for stabilizing the lever. Any yawngmoment acting on the frame '4 will produce a motion of rod 5T in one direction and a' contrary motion of rod 58, Which will 'produce forces acting in rods` 69 and T0, which will have components in the plane of Y-Y, equal and opposite, and `hence will cancel, while in the plane of X-X the components will Ybe additive'and will produce a net 'forceacting at lt'he pivotal connectiontof rodsii, .10 and lil, which will however be directly transmitted iromlsaid connection by means of va `rod 12 ito the yawing lmoment balance 15 of the "automatic self-recording ltype so `that upon any displacement of the common pivotal connection ofrods 69, 10, 1l', and 412, the balance. 1.5 will automaticallyl.produce va reaction force which will countenbalance Athe yawing moment and @hence `apply reacting Iforces backwards 'tolugs v55 and '56, tending fto serve as fa reaction against the existing yawing Vmoment and prevent rotation of the frame E4. I The actual displacement of the trame will at the most Y amount'toonlya fewonee'iihousandths yof an inch, so that fany 'forces arising due 'to deflection of 'the semi-umversal joints such as illustrated in Fig. 4 Will be of a negligible magnitude. Any forces ltransmitted by lugs 55and 5 due Ato side force such'as Y'of Fig. 7 will also be transmitted to rods '69 and 10 lsuch that 1the'comlfionents `o1- the forces Ain rods 69 and 'lil in the .plane of Y`-Y will be additive and 'will be transmitted by arm 1l as an 'axial force tending to displace the lfloating `lever in the Y-Y plane. 1t will 'be-apparent, however, that any side fonce acting at moment center 'D will produce a rolling `'moment L equal to Y, 1the side force, times distance H and this will xproduce an inequality 'in the forces transmitted through the pans @flirt rods 5 and s, and 1 and 8, and hence the dilTerence in the =fo1ces transmitted through lift rods Will appear as compolnents of `force in the plane of Y-Yfderive'd from the rods 23 la'nd26, inclusive, so that there will be a net component 'offorce acting in the plane of Y-Yvon levert!) at the pointof intersection off the rods in addition tothe force exerted through the arm l-I As seen Yin Fig. 8, thehorizontal components in Vthe plane of Y-Y Eof forces transmitted through rods 23 'to' l26, inclusive, due to the rolling moment oftheside .force'acts in theopposite directionffrom the for'ce -transinittedaxially through 'arm 7 I -due to the sidel force and, since the arm 'Il is positioned at a distanceA-i above the point of intersection of Athe -rods`23 tofZB, finelusive, Vby proper choiceof this distance,=the force in rod 'H may producean equivalentio'rce at the point of intersection of lift yrods 23 to 26, in elusive, which will be exactly equal and lopposite the net `for-cedue to side force rolling-"moments, and the lforce in Vrod 716 positionedva distance B1 above the point of attachment 'of rods 23 to 2t,Y inclusi-ve, vis a true measure `of the 'side force `being directly proportional to the `force in rod VT1. It is thus apparent thatpositioning va model above theaoating frame '4 will .produceiga rolling moment on trame '4,' due to the 'existence of any side `force -act'ingcnthe model, but yby means fof the compensating linkage employed,

:such rolling moment rod 18 will be zero and hence will not record a rolling moment on balance v8!! (Fig. 7) due to side force acting at distance H. However, any additional rolling moment other than that'due to `side force acting at distance H will be transmitted to the floating frame 4 and through the lift rods'5 to 8, inclusive, and appear as a force acting 'in the Y-Y plane on lever 3U at ,the juncture of rods 23 to 26, inclusive, which Will'be in excess Vof that previously described as dueto the rolling moment of the side force act- 'ing at distance y--I. Such additional force vwill vthen appear` as an axial load in rod 78, which will be transmitted directly to the rolling moment lbalance which will accurately record the value of the rolling moment about the moment center IJ and will produce `a reaction force acting in a re- Verse sense whichwill be transmitted to floating frame 4 so that no actual displacement of the `same will occur. AIt is seen that the method of compensating for rolling moment due to side .torce is substantiallythe same as that employed ier compensating for pitching moment due to drag.

In the force measuring system heretofore described, the forces. transmitted to the respective balances are each proportional to the loads -or moments to be measured, and suitable modifying mechanism is incorporated vin the balances to enable the same to directly record the actual numerical value of the respective-forces :and moments so that no computation workiwill be required, The balances are preferably of the beam "type, so that when in equilibriumv with the eX- ternal applied forces therewill be no actual displacement of the floating frame 4, any actual displacement being limited t-o such a small value that the geometry of the balance system will be unaffected. i

`The `'balance arrangement above Idescribed is so designed that the balances measure the forces Ian-d moments lon -a model or full size airplane 'about a point ll Which is a distance A from the lcenterline of litt rods 5 and 1 4and on the axis Y--Y, Figs. 2 and 3, and positioned distance H above the plane of rods -31 and 38, 51 :and 58. 'Ilhe .point il vis therefore fixed -by the original design land .is independent of the position lof the model in ra longitudinal plan-,e With respect to the point f, land therefore by shifting the model the forces and moments may be determined about any selected `axis 'on the model such as the quarter chord point on the wing lor Ithe axis on :the model passing through the point representing the center .or gravity fliocaftion of the full size airplane.

One form of construction enabling the model supports to be shifted to change the position of the model with respect to the fixed moment center il 'is illustrated lin Fig. 9, It is to be understood that this structure is intended to be used i-n place :orf .the model support 3, Figs. 2 yand 3, which was merely a showing of -a means for transierring forces land moments to the oating rframe 4. v

As seen in Fig. 9, the floating frame 4, corre- 4:s-poncl-ing to the same `ele'men't Figs. 2 aand 3, is provided witha-fcircularly apertured bottom plate 'Q13 which `receives a ring 92, and is provided with removable guides on its upper land lower side rto `'retain the. ring in assembled relation, suitfable` anti-friction -ibearing rollers (not shown) rbeing provided ,between the guides `95 and the plate fSiJ ,so 'that ythe -ring 92 may be rotated relative ,to fra-me 4 with a minimum of zfniction,

l l permitting lrotation of the model support system relative to the balance such as required for tests or the model in ylaw.

'Ilhe plate 92 is provided; iwith two symmetrically spaced T rails (only one shown) and a centrally ypositioned guide rail |02. 'Ilheguide rails |00 `an-d |52 serve to support identical longitudinally movable carriages |03 adapted to be adjusted in position along the rails lby any suitable means, such as lead screws |03a. Two i-dentical carriages |04 lare respectively mounted ifor sliding lateral movement on the carriages |03 and adapted to be simultaneously moved inward or outward trom the plane of symmetry by a lead screw arrangement or the like such as lead screws |04a.

Guides |05 are respectively secured to .the carriages |04 Iand serve .as guides for respective support struts |01 which, above the plane of frame 4, may project through the ring 92 and extend upward through |the frame 4 into tunnel testing chamber for attachment to the object bei-ng tested. The portions of the struts |01 projecting into the air stream 'are enclosed within streamline housings supported out of contact with the struts, the housing (not shown) being adjustable so as to be aligned with the struts. Each of the struts |01 i-s :provided with suitable attachment fittings to which the model or airp-lane being tested `may Ibe secured in -a wellknown manner.

The struts |01 Iare `universally .pivotally connected at their lower ends to fittings |08 which are respectively mounted for feeding movement each on one of two lead screws ||0 and which are threaded off the same hand land interconnectedy by gears ||2 .and adapted to be simultaneously rotated in opposite directions by means (not shown) to cause lan equal movement of struts |01 towards or yaway `from the plane or symmetry. The lead screws ||0 and are journal-led in brackets ||4 mounted on a plate |5 which is longitudinally slotted .as atv ||5 to serve `as a guide 'for an adjustable jattachment fitting ||1 adapted to be longitudinal-ly adjusted by means of a lead screw IIS. The iitting ||1 serves as a pivotal support for the lower end of Ia supporting strut which is adapted to be connected to the -model to be tested adjacent the rear portion to the fuselage. The plate ||5 is supported by plates |22 which unite with other plates |23 to iform a rectangular guide pedestal |25 slidalble vertically in a, hollow rectangular guide |21 which in turn is -slidlably supported on dovetail guides |29 Iformed in a yoke member |30 centrally Iapertured `as :at |3| to provid-e for axial movement of the guide |21. The guide |21 is provided with a bottom wall |33 which is provided with a journal bearing |34 or ya jack screw |35 which engages a threaded bore |36 in, a bottom w\all |31 of the pedestal so 'that manual or power rotation of jack screw will raise lor lower the pedestal |25 relative to guide |21 and yoke |30. A lead screw |30 is rotatably connected at its inner vend as at |39 to the guide |21 and at its outer end engages a threaded Ibore |40 in the yoke |30 so lthat Iby manual or `power rotation iof screw |38 the guide |21 and elements supported thereby may be llongitudinally yadjusted with respect to yoke |30.

The yoke |30 is supported by means of trunnions |42 (only one shown) swhich are rotatably journalled in bearings provided in lugs |43 formed integral with a semi-circular ring |45 rotatably mounted in a circular ring |46 which. Tigdly secured by means of braces |41 to the floating frame 4. Areversible electric motor |48 is mounted for ring |46 land geared by means of gears |49 and |50 to one od the trunnions |42 so that the yoke |30 may be tilted about the trun-nion axis and through struts |01 and |20 :act as a parallelogram linkage to cause a change in angle oi attack of the model equal to the angle of tilt of the yoke |30.

A .gear sector ring |45 meshes with a gear |52 driven by a reversible electric motor |55 which is mounted on a bracket |56 secured to stationary ring |46, and energizing of the motor causes the model support assembly to rotate in azimuth so that the model may be yawed with respect to the air stream.

Since the moment center of the balance system is a fixed point in space, it is necessary to position the model or airplane to be tested such that a predetermined moment axis on 'the airplane passes through the moment center of the balance. By means of the lateral spacing adjustment provided by lead screws ||0 and the struts |01 may be spaced for connection to the ttings on the wings or landing gear of the model, and similarly lead screw ||8 provides for longitudinal adjustment of strut |20 so that the latter may be readily connected to a third supporting point on the model or airplane being tested. It is also essential that the selected axis of the model be co-planar with the axis of the trunnions |42 and this may be obtained by shifting the guide |21 and pedestal |25 by means of lead screw |38. By raising or lowering pedestal |25 relative to guide |21 by adjusting jack screw |35, the model may be adjusted in the vertical plane.

The longitudinal axis of the model being tested may be aligned with or yawed with respect to the air stream by rotation of the model support assembly by motor |55, and the angle of attack may be changed by rotation of yoke |30 by motor |48 as previously described.

It will be apparent to those skilled in the art that variations may be made in the structure illustrated and described Without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In an aerodynamic balance for Wind tunnels, a model support, a floating frame secured to said support and adapted to move in translation along or rotate about mutually perpendicular lift, drag and rolling coordinate axes, respectively, due to forces exerted on a model being tested, a. floating lever, linkage for transmitting forces in the plane of the lift axis from said frame to said lever and including links connected at a common point to said lever such that the sum of the components of force in said links along the axis of said lever equal the lift forces on said support and the sum of the components of force in said links acting normal to said lever in the plane of the second of said coordinate axis being a measure of the moment on said frame about the third coordinate axis, means connected normal to said lever at the :point of connection of said links and connected to la moment balance, means for transmitting a force in the plane of said second coordinate axis from saidframe to said lever, said last named means being connected to said link at a point spaced from the means connected to said moment balance such as to apply a force to said lever just equalizing the effect of a force thereon due to the moment produced by the force in the plane of the second coordinate axis and a ramasse lsaid .second coordinate axis. i

2. In a Wind tunnel balance system for measuring forces and moments on a model being tested, a model support, a floating `frame secured to said support and having six degrees "ci free- Ydom withrrespect to three mutually perpendicular lift, drag aand rolling coordinate axes, '.a Vpfloating lever, a lift 'balance connected to said lever,link- Aage connected to said lever at af cOmmonEpOint, said linkage being adapted to apply components of force therein along the axis of said lever and to apply components of force in planes at right angles to each other and normal to said lever at said common point as a measure of pitch and rolling moments respectively acting on said frame, pitch and rolling moment balances respectively connected to said lever common point in the respective planes of the application of the respective moment force components thereto, separate linkages for transmitting drag and side forces from said frame to said lever, said separate linkages being respectively7 connected to said lever at points spaced from said common point and adaptand movable along and rotatable about mutually f' perpendicular lift, pitch and roll coordinate axes respectively, a floating lever, means for transmitting a force to said lever from said frame, which force is a measure for the moment acting about one of said axes other than the vertical or lift axis,

a moment balance connected to said lever at the point of connection of said last named means, a force measuring balance connected to said lever at a point spaced from connection of said moment balance thereto, a force transmitting linkage for transmitting forces acting on said frame in the plane of the other of said coordinate axes to said lever at a point intermediate the connection of the other of said balances therewith such that the reaction produced at the point of connection of said moment balance to said frame Will be equal and opposite the force transmitted to said moment balance due to the moment oi the force in the plane of said other co-ordinate axis.

4. In an aerodynamic balance system for Wind tunnels ci the character wherein a model is supported in the air stream on a support secured to a floating frame below the model, a pitch balance, means including a floating lever interconnecting said frame and said balance, a drag balance connected to said lfloating lever at a point spaced from the connection of said pitch balance thereto, means for transmitting drag force from said frame to said lever and to said drag balance, said last named means being connected to said lever so as to subtract from the force transmitted to said pitch balance a force equal to the effect of the pitching moment on said frame caused by the drag force.

5. In an aerodynamic balance system, a model support for supporting a model to be tested, a oating frame secured to said support, a pitching moment balance, linkage interconnecting said pitching moment balance and said frame, a drag balance, linkage means interconnecting said drag 121 Abalance and said =`frame for transmitting drag iforces acting on 'the lframe to .thefbalance, and a compensating lever .connectedin common to I each `/oisaid linkages `1or applying a correcting fior-ce :derived from said ldrag linkage to said pitching finement rbalance linkage to .prevent the 'force Vdue to the pitching moment-dueto thedrag force acting vontthe lmodel support from'being transmitted 1to said pitching 'moment balance.

U6. Inan 'aerodynamic ybalance system,.a model support for supporting a model to be tested, a floating `frame'securedlto said support, a pitching moment balance, a rolling moment balance, a drag balance and a side force balance, separate force transmitting means interconnecting said frame and each of said balances and a compensating iioating lever connected in common to each of said force transmitting means and operative to prevent the pitching moment due to drag force acting on said support and rolling moment due to side force act'ing on said support from being transmitted through said frame and asso- -ciated force transmitting linkages to said pitching moment and rolling moment balances respectively.

'7. In a Wind tunnel balance of the character described a model support, a floating frame secured to said support and having six degrees of freedom With respect to three mutually perpendicular coordinate axes intersecting at a fixed moment center or point in space above said frame, separate yaW, pitch and rolling moment balances for measuring the moments about the respective axes, linkage means interconnecting the frame and balances including a floating compensating lever connected in common between said drag, side force, pitch and rolling moment balances such that the moments on the frame due to the drag and side force acting through the moment center are subtracted from the moments transmitted to the pitch and rolling moment balances whereby said balances measure the respective forces and moments acting on said model support with respect to said moment center, and means for shifting said model support vertically and longitudinally with respect to said frame to thereby shift the model with respect to the said fixed moment center.

8. The structure as claimed in claim l0, in which the model support is also rotatable in azimuth to vary the angle of the longitudinal axis of the model with respect to the direction of the air stream. l

9. In an aerodynamic balance for Wind tunnels, a model support, a floating frame secured to said support and adapted to move in translation along and rotate about mutually perpendicular lift, drag and rolling coordinate axes, respectively due to forces exerted on the model 'being tested, a floating lever universally pivotally supported at one end from a lift force Weighing arm, said 4lever being movable along its own axis as Well as being movable in any plane normal to its axis, rods universally connected to said floating lever so that their lines of action intersect at a common point at the axis of said lever, said rods fbeing inclined to form a pyramid to transmit components of forces to said lever parallel and normal to `the axis thereof, linkage connecting the iioating frame to said rods to transmit all forces thereto `due to lift, pitching and rolling moments acting on the model, pitch and rolling moment balances connected to said floating lever in planes at right angles to each -other and intersecting at the point of connection of said rods to the floating lever,

15 16 and separate drag and side force load transmit- 1 ting means connected to said oating frame and REFERENCES CITED Connected t0 said floating leVer at points spaced The following references are of record in the from the connections of the moment balances me of this patent: thereto such that the transmitted drag and side 5 forces produce forces, at the connections of the UNITED STATES PATENTS pitch and rolling moment balances respectively-,t0 Number Name Date the naat-ing lever, neutralizing the eiect of the 1,404,920 zahm Jan, 31, 192.2 drag and side for-ces on the pitching and rolling 1,710,135 zahm Apr. 23, 1929 moment forces exerted on the floating frame by 10 1,930,195 Gerhardt et al, Nov, 13, 1934 the model. 2,353,033 Hem July 4, 1944 HERBERT M. HEUVER. 

